In a packet-based wireless communication system, if an MS has not transmitted or received packets for a predetermined time, it enters a power saving mode, i.e. a sleep mode, to minimize its power consumption.
The MS generally uses a timer to determine the time to enter the sleep mode. In the absence of packet transmission and reception for a predetermined time period measured from a reference time, the MS requests transition to the sleep mode to a Base Station (BS). Upon receipt of a response to the transition-to-sleep mode request from the BS, the MS enters the sleep mode.
FIG. 1 illustrates a signal flow for entering a sleep mode using a timer at an MS in a conventional packet-based communication system.
Referring to FIG. 1, an MS 101 monitors whether packets have been transmitted or received during a time period measured from time T1, indicated by a dotted line, after a timer that includes a predetermined value starts at time T1. The MS 101 receives a downlink packet from a BS 103 at time T2. Thus the timer that has started at time T1 is terminated and is reset at time T2. The MS 101 then monitors packet transmission and reception during the predetermined timer period starting at time T2. Because an uplink packet is generated at time T3, the timer that has started at time T2 is terminated and is reset at time T3. There is neither packet transmission nor packet reception during the predetermined timer period from time T3. Therefore, the MS 101 requests transition to the sleep mode to the BS 103. Upon receipt of a response from the BS 103, the MS 101 enters the sleep mode. The timer value is normally fixed.
However, packets of some types transmitted from an MS always require responses. For example, such packet types are Transmission Control Protocol (TCP) packets or Dynamic Host Configuration Protocol (DHCP) packets. If the MS operates a timer that includes a fixed timer value to receive a response for such a packet, it may fail to receive the response, thus losing the response packet.
For example, when the timer value is fixed to 30 seconds and a response to a TCP packet transmitted by the MS reaches the MS 40 minutes later, the MS has already entered the sleep mode and thus does not receive the response.
With regard to a DHCP packet, the MS should transmit a DHCP Request packet to a BS in order to get an Internet Protocol (IP) address, receive a DHCP packet in response to the DHCP Request packet from the BS, and check whether the received DHCP packet includes an Acknowledgement (ACK) in a DHCP procedure. However, if the MS uses a timer set to a fixed timer value, the timer expires before the MS receives an ACK for the transmitted DHCP Request packet. Thus the MS may enter the sleep mode. Even though the MS retransmits the DHCP Request packet to the BS, the DHCP Request packet may not be processed normally.
Alternatively, in a service using packets that are generated more often than the fixed timer value (e.g. a text message service), the MS is highly probable to receive a response packet before timeout, which makes power saving difficult.
As described above, the conventional technology that uses a fixed timer value does not take into account characteristics of packets that an MS transmits or receives. The MS may fail to transmit or receive packets successfully, or the MS may not enter the sleep mode. As a consequence, the power consumption of the MS may be increased.